1. Field of the Invention
The invention relates to an improved process of producing vinyl acetate (VA) utilizing a catalytic reactor equipped with a filter and distribution bed.
2. Description of the Related Art
It is known to produce VA by the vapor phase reaction of ethylene, oxygen, and acetic acid using a catalyst, e.g., comprising metallic palladium and gold supported on an inert porous carrier. Such reaction may be carried out in a reactor having the configuration of a tube and shell heat exchanger, i.e., comprising a plurality of tubes, each containing a bed of catalyst and supported between two "sheets" or rigid plates, with the tubes remaining open at each end. The tube and sheet assembly is enclosed in a shell such that the tubesheets separate two end portions of the interior of the shell serving as the inlet and outlet areas for the entering reactants and the exiting products respectively of the VA reaction. The space between the sheets defines the midportion of the interior of the shell through which heat exchange medium, e.g., hot water, surrounding the portions of the tubes containing the catalyst beds, is circulated to absorb much of the heat generated by the exothermic reaction.
A problem associated with the production of VA in a reactor of the type described is that the feed gases in addition to non-condensable recycle gases including ethylene, carbon dioxide, methane, oxygen and others, along with vaporized acetic acid, and heavy ends such as higher esters of acetic acid, may also contain, continuously or intermittently, non-volatile components such as inhibitor residue and polymers, and/or liquid acetic acid. The non-volatile components and/or liquid acetic acid are entrained in the vapor flow from the acetic acid vaporizer and propelled onto the inlet tubesheet of the reactor and into some or all of the tubes. This results in partial plugging of some of the tubes and tneven flow distribution among the reactor tubes, which in turn, results in suboptimum catalyst performance including `runaway tubes`, i.e., reactor tubes which are operating in a mode making mostly carbon dioxide rather than VA. The distribution of the non-volatiles and liquid acetic acid across the tubes may not be uniform so that some of the tubes become more plugged than others. The plugging of the tubes is essentially non-reversible, so that whenever entrainment occurs, the damage that is done remains for the life of the catalyst, unless the VA unit is shut down for reactor entry to vacuum some of the catalyst from the inlet of the tubes and replace it. Thus, the plugging of the tubes seriously reduces the efficiency of the reactor and any expedient which significantly reduces such plugging would be very valuable.